US2869020A

US2869020A - Coaxial coupling for traveling-wave tubes

Info

Publication number: US2869020A
Application number: US532323A
Authority: US
Inventors: Sensiper Samuel
Original assignee: Hughes Aircraft Co
Current assignee: Raytheon Co
Priority date: 1955-09-02
Filing date: 1955-09-02
Publication date: 1959-01-13
Anticipated expiration: 1976-01-13

Description

Jan. 13, 1959 s. SENSIPER COAXIAL COUPLING FOR TRAVELING-WAVE TUBES Filed Sept. 2, 1955 ATM/EWEV COAXIAL COUPLING FOR TRAVELING-WAVE TUBES Samuel Sensiper, Los Angeles, Calif., assignor to Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware Application September 2, 1955, Serial No. 532,323 4 Claims. Cl. 315-35) The subject invention relates to traveling-wave tubes in general, and more particularlyto an improved means for coupling microwave energy to the slow-wave structure in a traveling-wave tube.

Heretofore a rectangular waveguide has been used for coupling microwave energy to the type of slow-wave structure known as a contrawound helix. Such a system has the disadvantages of narrow bandwidth and of being inflexible in adjustment or adaptability to different conditions of operation.

It is, therefore, an object of the present invention to provide a broadband system for coupling microwave energy onto a stub loaded contrawound slow-wave struc ture.

It is anotherobject to provide such a coupling which is flexible and adaptable to either coaxial lines or waveguide lines.

It is a further object to provide such a coupling which mechanically simple and easy to fabricate.

It is still a further object to provide such a device which provides a means for varying many of the parameters of coupling from the slow-wave structure to the input and output transmission lines.

Briefly, objects are achieved in the following manner. The inner conductor of a coaxial line is coupled at one point or two points, directly to the input end of a contrawound slow- A wave structure. The coaxial line may then be matched easily to any desired transmission line by methods well known in the art.

The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description considered in connection with the accompanying drawing in which an embodiment of the invention is illustrated by way of example. It is to be expressly understood, however, that the drawing is for the purpose of illustration and description only, and is not intended as a definition of the limits of the invention.

In the drawing:

Fig. 1 is .a View of a traveling-wave tube illustrating one embodiment of the present invention;

Fig. 2 is a cross-sectional view of another embodiment of the device of Fig. 1;

Fig. 3 is a view of a further embodiment of the present invention;

Fig. 4 is a cross-sectional view of still a further embodiment of the device of Fig. 3; and

Fig. 5 is a schematic view of a variation of the struc ture of Fig. 2.

Referring now to the drawing and specifically to Fig. l, traveling-wave tube is shown including a glass envelope 12 disposed between an electron gun 14 and a collector electrode 16. A typical contrawound slow-wave structure 18 is shown disposed along the path of the electron beam from gun 14 to collector 16. Slow-wave nited States Patent 0 in accordance with the present invention, these structure 18 consists of a series of spaced circular elements 15 interconnected by longitudinal elements or rods 17 extending from opposite points on circular elements 15 so that the rods 17 are disposed in a plane. Input coaxial line 20 is shown to have its inner conductor 21 coupled through metal shield 22 to the point on the input end of. structure 18 directly opposite the first longitudinal element of the structure. A microwave window 24 provides a pressure seal for the evacuated volume within the tube. In like manner coaxial conductor 26 is coupled to the output end of structure 18 such that the center conductor 27 is mechanically connected to the point on the output end of the structure which is directly opposite the last longitudinal member of the structure. Again, a microwave window 28 provides a pressure seal for the vacuum within traveling-wave tube 10. Solenoid 36] provides a longitudinally magnetic field for confining and focusing the electron stream within structure 18.

Referring to Fig. 2, .there is shown in cross section another embodiment of the tube of Fig. 1 taken through the first circular member of the slow-wave structure of a similar tube. Input coaxial :line 28 is split at junction 32 and energy traveling therealong is equally distributed to

inner conductors

34 and 36 which pass through metal shield 23 and are directly coupled to structure 18 at the symmetrical, with respect to point 39 which rep resents the first longitudinal member of structure 18, points 40 and 42.

Referring to Fig. '3, there is shown a system in accordance with the present invention for coupling microwave energy onto structure 18 using a second contrawound slow-wave structure 44 which may be similar to structure 18 and which is disposed concentrically about structure 18 in such a manner that at each point the inductive reactance is equal and opposite to the capacitive reactan-ce for electromagnetically coupling microwave energy between structure 44 and structure 18. Coaxial conductor 46 is arranged such that its outer conductor is coupled to metal shield 48 and its inner conductor 58 is coupled through shield 48 to structure 44 are point opposite the first longitudinal member of structure 44.

Referring to Fig. 4, there is shown another embodiment of the device of Fig. 3 in a cross seetional view taken through the first circular member of the contrawound slow-wave structure of a similar tube. Input conductor 46 divides at junction 52 so that energy traveling along center conductor is evenly divided between

inner conductors

54 and 56 which each pass through metal shield 49 and are coupled directly to synmmetrical, with respect to point 55 which represents the first longitudinal member of structure 44,

points

56 and 58.

Fig. 5 shows schematically a generalized version oi the structure shown in Fig. 2, in which the first circular member of structure 18is parted by an arbitrary gap 41 between points 40' and 42 opposite point 39 which represents the juncture of the first circular member with the first longitudinal or stub member. Points 48 and 42 are asymmetrically disposed with respect to point 39 and couple, respectively, inner conductors 34 and 3 to structure 18. Interposed in conductor 34' is a variable delay line 35; and in conductor 36' is variable delay line 37.

In operation of the example of the present invention, as shown in Fig. 1, microwave energy is coupled symmetrically to contrawound slow-wave structure 18. The resulting traveling wave is caused to grow or be amplified as it propagates along the structure; and the microwave energy is coupled out of the structure onto coaxial line 26 at the output end of traveling-wave tube 10 in the same manner.

It may be desirable to adjust or control many of the ascents properties of the coupling from the coaxial line to the contrawound slow-wave structure by feeding the structure at different points along the periphery of the first ring of the structure, but since the energy fed to the structure must be in phase when it reaches point 39, shown on Fig. 2, the structure is fed at two points 40 and 42 which are symmetrical with respect to point 39.

The structure of Fig. 3 represents an embodiment in which the R. F. energy is electromagnetically coupled to the contrawound slow-wave structure 18 by use of a second slow-wave structure 44 which is disposed as shown about the input end of structure 18. This type of coupling is known as through-vacuum or coupled helices coupling. The operation of this embodiment is similar to that of the embodiment shown in Fig. 1 except that the input energy is used to launch a wave along structure 44 which is long enough so that substantially all the energy of the traveling wave of structure 44 is coupled to a traveling wave in structure 18. This traveling wave then is caused to grow or be amplified along the length of structure 18.

In the embodiment of Fig. 4 energy is fed to the outer structure 44 at a point different from the point opposite 55 and, as discussed in connection with Fig. 2, it is fed symmetrically at

points

56 and 58.

In the operation of the variation of the invent-ion as shown in Fig. 5, microwave energy is fed to junction 32 where it is divided and dispersed along

conductors

34 and 36 toward points 40' and 42' on the input end of structure 18. Point 40 and 42' may be asymmetrically disposed and the magnitude of delay of delay lines 35 and 37 adjusted to provide in-phase currents along the first longitudinal member of the structure. Further adjustment of the coupling parameters may be provided by changing the position and length of gap 41.

There has thus been disclosed a system for coupling the coaxial line to the slow-wave structure of a travelingwave tube which is very broadband and which has great flexibility both mechanically and electrically since many techniques are well known in the art for coupling the coaxial line herein described to any other type of microwave transmission line. Further, the structure disclosed is mechanically simple and easy to build. Also, the device of the present invention provides a heretofore unknown means for varying coupling parameters and, in accordance with the structures shown in Figs. 3 and 4, the present invention provides through-vacuum coupling for use with contrawound coupling slow-wave structures.

What is claimed is:

1. A broadband traveling-wave tube comprising a contrawound slow-wave structure having a first transverse circular member and a first linear longitudinal member coupled thereto at a point on the periphery of said first circular member; coaxial coupling means for coupling microwave energy from a transmission line to said slowwave structure comprising: a coaxial transmission line; a junction for said line; a first and second point on the first circular member of the contrawound slow-wave structure which are disposed symmetrically on the periphery of said first circular member with respect to the point at which the first longitudinal member is attached thereto; a first and a second coaxial transmission line, said first coaxial transmission line being coupled between said first point and said junction, said second transmission line being coupled between said second point and said junction in a manner to feed said slow-Wave structure at a point not directly opposite said first longitudinal member while nevertheless providing means for feeding said slow-wave 4 structure in a manner such that currents from said first and second transmission lines in said first longitudinal member are in phase.

2. The structure according to claim 1 in which there is a gap in the periphery of said first circular member in that portion of said first circular member between said first and second points opposite said point at which said first longitudinal member is attached to the periphery of said first circular member.

3. In a broadband traveling-wave tube, an envelope, at contrawound slow-wave structure within said envelope and having a first transverse circular member .and a first linear longitudinal member coupled thereto at a point on the periphery of said first circular member, whereby said structure is the electrical equivalent of a contrawound helix; and coaxial coupling means for coupling microwave energy from a transmission line to said slow-wave structure comprising a first coaxial transmission line; a junction for said first line; a first and second point on said first circular member of said contrawound slow-wave structure, said points being disposed symmetrically on the periphery of said first circular member with respect to the point at which the first longitudinal member is attached thereto; a second and third coaxial transmission line coupled to said first line and entering from the side of said envelope, said second coaxial transmission line being coupled between said first point and said junction, said third transmission line being coupled between said second point and said junction to feed said slow-wave structure at a point not directly opposite said first longitudinal member while providing means for feeding said slow-wave structure in a manner such that currents from said second and third transmission lines are in phase in said first longitudinal member.

4. A broadband traveling-wave tube comprising: an envelope; a contrawound slow-wave structure within said envelope having a first transverse circular member and a first linear longitudinal member coupled thereto at a point on the periphery of said first circular member whereby said structure is the electrical equivalent of a unifilar contrawound helix; and coaxial coupling means for coupling microwave energy from .a transmission line to said slowwave structure comprising: a first coaxial transmission line; a junction point for said line; first and second points on said first circular member of said contrawound slowwave structure, said points being disposed on the periphery of said first circular member and being separated thereon by a finite distance; second and third coaxial transmission lines coupled to said junction point of said first line and entering from the side of said envelope; said second coaxial transmission line being coupled between said first point and said junction point; said third transmission line being coupled between said second point and said junction point to feed said slow-wave structure in a manner such that currents from said second and third transmission lines combine in phase in said first longitudinal member.

References Cited in the file of this patent Great Britain Mar. 12, 1952